The red came just seven minutes later, as Williamson was ejected in the 56th minute with a second yellow card. The dismissal forced Portland to play a player short the rest of the match, but Western New York could not capitalize on the advantage.

"When Portland's down a player for 35 minutes and we're not able to put a ball in the back of the net in that time, Portland deserves it," Lines said.

Former Flash star Sinclair scored in stoppage time on a pass from 72nd-minute substitute Alex Morgan, who had been held out of the starting lineup because of a knee ailment.

Sinclair headed directly to the few dozen vocal Thorns supporters stationed behind the goal to celebrate and blow kisses after effectively sealing the first year team's championship.

"I was going to go over to our bench but I thought, 'I'm not running that far,'" Sinclair said.

Playing with the advantage, the Flash attempted 18 shots, nine more than the Thorns. Portland goalkeeper Karina LeBlanc made seven saves in the short-handed win.